Heat dissipating apparatus having micro-structure layer and method of fabricating the same

ABSTRACT

A heat dissipating apparatus has a micro-structure layer. Two highly heat conductive members are provided, each having structured patterns. A highly heat conductive material is coated on the structured patterns by injection molding for forming a micro-structure layer. The two highly heat conductive members are assembled to form a heat dissipating apparatus having a micro-structure layer. The heat dissipating apparatus includes a main body composed of the highly heat conductive members. The main body forms an accommodating cavity, and inner surfaces of the accommodating cavity form the micro-structure layer. A working fluid is filled into the accommodating cavity for transferring heat from a heat absorbing surface to a heat dissipating surface.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of U.S. application Ser. No. 10/995,480, filed Nov.24, 2004, which claimed Priority from Taiwanese application No.093118983, filed Jun. 29, 2004, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a heat dissipating apparatushaving a micro-structure layer and method of fabricating the same, andmore particularly, to a heat dissipating apparatus having amicro-structure layer and method of fabricating the same employing aliquid-gas phase transition to dissipate heat.

2. Description of the Related Art

During the last decades, semiconductor fabrication techniques have bothreduced the size and increased the functionality of electronic devices,but problems in terms of power consumption, heat dissipation, andreliability have inevitably derived from the process of integrating theelectronic devices.

The main reason for the limited reliability of the above devices is thatthe electronic devices are driven by electricity power that is not fullyutilized, and the unused portion of power is converted into heat energy,which dramatically raises the temperature of the whole systemincorporating these devices. In the case that the operating temperaturegoes beyond the range permitted, erratic operation, system failure, andeven damage may occur. For the new generation of high-density electronicproducts, the computation speed and operating frequency of the internalelectronic devices thereof is much higher than conventional products.Thus, the amount of heat generated in the course of operation issignificantly huge to easily result in their operating temperatureexceeding the permitting range. Compounding the problem, along with thetrend of miniaturized electronic devices, heat dissipating apparatus hasshrunk the size as well to accommodate the desire for smaller products,which presents a big challenge to the fabricating technology in thisfield in terms of effective heat dissipation and product reliability.

To address the aforementioned problems, a passive cooling mechanismwhich adopts a liquid-gas phase transition in the fluid is employed inconventional technology. As illustrated in FIG. 5, with liquid-gas phasetransition and capillary action in a heat pipe, the heat from a heatabsorbing end (heat source) 50 is conducted via evaporation of theliquid to a heat dissipating end 51, and further with condensation ofthe vapor and capillary pull of the capillary structure, a circulatedmovement is provided for continually dissipating the heat generated bythe electronic devices. Both Taiwanese Patent Publication of 528151 and501722 disclose such heat dissipating apparatus incorporating the aboveheat pipe.

The heat dissipating efficiency of the above apparatus is determined bythe capillary structure. If the dimensional precision and distributionof the capillary structures fail to comply with design requirements, theefficiency of the vaporized fluid moving from the heat-absorbing end tothe heat-dissipating end may be degraded, and the efficiency ofvaporized fluid returning to the heat dissipating end to bere-circulated after heat dissipation may also be degraded. While suchheat dissipating apparatus is targeted for using on the miniaturizedelectronic devices, having the capillary structures dimensioned inmicron (μm) scale adds more difficulty to precisely control thefabricating method.

U.S. Pat. No. 4,046,190 discloses a method of fabricating the capillarystructure by means of sintered powdered metal. The method is to firstlyspread a layer of highly heat conductive metal particles, such ascopper, and then sinter under high temperature to form the desiredcapillary structure. However, a serious drawback associated with thefabrication method is found in the actual production, since thedimension of the capillary structure is not precisely controlled by suchsintering method. For a capillary structure with dimensional precisionrequired at the μm scale, the final sintered product usually does notmeet the dimensional precision as required in the original design.Therefore, the heat dissipating efficiency is significantly degraded.

To solve the above problem, an injection molding process is adopted inthe conventional technology, where injection molding process isperformed using sintered copper powder. With characteristics of theinjection molding process, the desired capillary structure or channelthat fulfills the highly precise geometric dimension requirement isformed, so as to meet the precision requirement of the capillarystructures. However, the process described above only solves the problemassociated with forming the capillary structure. Other drawbacks remainto be solved, such as the density of the applied copper is relativelylow compared to regular plated copper due to the high temperature usedin injection molding resulting in a much lower thermal coefficient.Therefore, although heat can be dissipated by liquid-gas phasetransition according to the process above, the efficiency of heatdissipation as a whole still awaits further improvement, and currentneeds for heat dissipating of electronic devices are not satisfied.

Consequently, it is desirable to develop a method for fabricating a heatdissipating apparatus having such a capillary structure layer that canincrease the heat dissipation efficiency of the apparatus, wherein thefabricating method is simple and adaptable to rapid mass production.

SUMMARY OF THE INVENTION

To overcome the above drawbacks of conventional technology, an objectiveof the present invention is to provide a heat dissipating apparatushaving a micro-structure layer and a method of fabricating the same,which increase the heat dissipating efficiency thereof.

Another objective of the present invention is to provide a heatdissipating apparatus having a micro-structure layer and method offabricating the same, which fabricating method is simple and adaptableto mass production.

Still another objective of the present invention is to provide a smallscale heat dissipating apparatus having a micro-structure layer andmethod of fabricating the same.

In accordance with the above and other objectives, the present inventionproposes a fabricating method for a heat dissipating apparatus having amicro-structure layer. The method involves providing two highly heatconductive members, surfaces of the two substrates comprising structuredpatterns; performing injection molding along the structured patterns ofthe highly heat conductive substrates to form a micro-structure layer onsaid structured patterns, wherein the micro-structure layer is composedof highly heat conductive material; and assembling said two highly heatconductive substrates to form an accommodating cavity, wherein theaccommodating cavity is filled with a working fluid.

In an alternative embodiment, the fabrication method of a heatdissipating apparatus having a micro-structure layer comprises thefollowing steps: providing two highly heat conductive substrates areprovided, surfaces of the two substrates comprising structured patterns;forming a highly heat conductive layer on the structure patterns of thehighly heat conductive members; performing printing process on saidhighly heat conductive layer to form a micro-structure layer; andassembling said two highly heat conductive members for forming anaccommodating cavity, wherein the accommodating cavity is filled with aworking fluid.

Accordingly, the present invention proposes a heat dissipating apparatushaving a micro-structure layer. The heat dissipating apparatus comprisesof a highly heat conductive member having an accommodating cavitytherein; a micro-structure layer formed on an inner wall of theaccommodating cavity by injection molding, and the micro-structure ismade of highly heat conductive material; and a working fluid for fillingthe accommodating cavity.

The above micro-structure layer is a capillary structure, whichgenerates a capillary pull for the working fluid that is adhered to andin contact with capillary structure, so as to move the working fluidalong an edge of the capillary structure. The capillary structure may bea plurality of parallel grooves or mesh structure with no particularlimitation on their manner of arrangements.

The highly heat conductive material may be copper, silver, aluminum, andother heat conductive metals. And the highly heat conductive material isthe same as the material for forming the first and second substrate s.The first and second substrates are both made of a highly-dense block,and the first and second substrates have a heat absorbing surface and aheat dissipating surface, respectively.

According to the fabricating method of the present invention, a metalsubstrate with high heat conduction coefficient is provided, which isfurther form as a desired high precision micro-structure layer byinjection molding or printing. With rapid heat conduction of thesubstrate and liquid-gas phase transition theory employed in theaccommodating cavity, the dissipated heat is rapidly discharged to solvethe problems mentioned above of the conventional heat dissipatingapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included herein provide a further understanding of theinvention. A brief description of the drawings is as follows:

FIGS. 1A to 1C are flow diagrams illustrating a fabrication method for aheat dissipating apparatus in accordance with the present invention;

FIG. 2 is an elevation view of a micro-structure layer of the heatdissipating apparatus in accordance with the present invention;

FIGS. 3 and 4 are cross-sectional views of the heat dissipatingapparatus in accordance with other embodiments of the present invention;and

FIG. 5 is a schematic view of a liquid-gas phase transition type of theconventional heat dissipating apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1A to 1C illustrate the fabrication method of a heat dissipatingapparatus having a micro-structure layer in accordance with the presentinvention. Firstly, referring to FIG. 1A, a first substrate 10 and asecond substrate 20 of equal dimension are respectively provided. Bothof the first substrate 10 and second substrate 20 are made of ahighly-dense metal block, and the metal block may be a highly heatconductive material such as copper, silver, aluminum, and so on. Thefirst substrate 10 is defined with a first opening 11 having an innerwall formed with a geometrically structured pattern 12, such as theillustrated projections, such that differing profile heights areprovided in the inner wall of the first opening 11. In contrast, a heatabsorbing surface 13 is defined on an outer surface of the firstsubstrate 10 opposite to the first opening 11. The second substrate 20comprises a similar structure to that of the first substrate 10. Thesecond substrate 20 is defined with a second opening 21 having an innerwall formed with a geometrically structured pattern 22 positionallyopposite that of the structured pattern 12 of the first opening 11. Incontrast, a heat dissipating surface 23 is defined on an outer surfaceof the second substrate 20 opposite to the second opening 21.

Then, referring to FIG. 1B, a metal injection molding (MIM) process isperformed, wherein highly heat conductive material (such as copper,silver, or aluminum) of the same kind as that of the first substrate 10and second substrate 20 is made of metal powder and injected under hightemperature. The above metal powder is injected into the first opening11 and second opening 21, for forming a micro-structure layer 30 tightlycoating said inner walls of the first opening 11 and second opening 21,respectively. As illustrated in FIG. 1B, the micro-structure layer 30 isevenly formed on the entire inner wall of the first opening 11 andsecond opening 21, and conforms to differing heights on the structuredpatterns 12, 22. Simultaneously, the inner walls of the first opening 11and second opening 21 that are respectively perpendicular to the heatabsorbing surface 13 and heat dissipating surface 23 are also formedwith said micro-structure layer 30.

The micro-structure layer 30 functions as a wick or capillary structureto generate a capillary pull for a working fluid that is adhered to andin contact with the capillary structure, so as to move the working fluidalong an edge of the capillary structure 30. The capillary structure 30may be a plurality of parallel grooves or a mesh structure, and there isno particular limitation on the arrangement of grooves or meshstructure, as long as the highly heat conductive capillarymicro-structure layer is formed by injection molding. Referring to FIG.2, an elevation view of the capillary structure 30 according to onepreferred embodiment is illustrated. The capillary structure 30 iscomprised of a plurality of parallel grooves, wherein the slashedportion is the capillary structure formed by injection molding, and thenon-slashed portion represents the inner walls of the first opening 11or second opening 21.

Referring to FIG. 1C, after injection molding process is performed toform the capillary structure 30, the first substrate 10 and secondsubstrate 20 are assembled together in a manner such that the firstopening 11 is brought near to the second opening 21, so that the firstopening 11 communicates with the second opening 21 to form anaccommodating cavity 35 therebetween. The accommodating cavity 35 isfilled with a working fluid 40. Therefore, the inner walls of the firstopening 11 and second opening 21 forms the inner wall of theaccommodating cavity 35, said entire inner wall of the accommodatingcavity 35 is thus evenly distributed with the capillary structure 30,and the working fluid 40 fills and adheres to the bottom and lateralsides of the capillary structure 30, so as to complete fabrication ofthe heat dissipating apparatus having micro-structure layer.

The aforementioned working fluid 40 is provided for transmitting heat.So, the working fluid 40 may be selected according to the requirement ofdissipating environment, for example, a fluid having an appropriateboiling point or condensation point, such as liquid water, acetone,liquid nitrogen, or ethanol may be selected.

According to the fabricating method of the present invention, theproblems associated with conventional method for fabricating the heatdissipating apparatus are solved. Since the main body of the heatdissipating apparatus of the present invention is composed of the metalsubstrates 10, 20 with high density and high coefficient of heatconduction, the apparatus is very efficient in heat dissipation. Inaddition, the first and second substrates 10, 20 are further providedwith the capillary structure layer 30 formed by injection molding tobenefit from the injection molding process is made use of to preciselycontrol the dimension and geometrical configuration of themicro-structure layer 30. The present invention successfully solves theproblems that a precise capillary structure cannot be formed by means ofsintered powdered metal and the problem of the main body having a lowcoefficient of heat conduction by fabricating the whole heat dissipatingapparatus by injection molding.

In addition, the fabrication method of the present invention employsinjection molding only to form the desired micro-structure layer 30 onthe first and second substrates 10, 20, which is simple and adapted tomass production. The heat dissipating apparatus of the present inventioncan be made to a considerably small scale, thus keeping up with thetrend of miniaturization of electronic elements

Alternatively, in addition to injection molding, the micro-structurelayer 30 of the present invention can also be formed by press-printing.A highly heat conductive material layer is firstly formed on thestructured patterns 12, 22 of the first and second substrates 10, 20.Said highly heat conductive material layer is then subjected to aprinting process to form the micro-structure layer 30.

Referring to FIG. 3, a ring-shaped frame 45 having the same peripheralshape configuration with the first and second substrates 10, 20 isprovided and arranged between the first and second substrates 10, 20,for interconnecting the first and second substrates 10, 20, andincreasing the height of the heat dissipating apparatus to enlarge theaccommodating cavity 35.

It is not necessary for the structured patterns 12, 22 of the first andsecond substrates 10, 20 to be identical. Referring to FIG. 4, in analternative embodiment, the first and second substrates 10, 20,respectively may comprise structured patterns 12, 22 of a differentconfiguration, as long as an accommodating cavity 35 is formedtherebetween after the first and second substrates 10, 20 are assembled.

Therefore, the heat dissipating apparatus fabricated by the fabricationmethod of the present invention meets the heat dissipating demands ofsmall scale electronic devices. The heat dissipating apparatus isaffixed on a heat source (such as an electronic device), and the heatabsorbing surface 13 is contact with said heat source. The heatabsorbing surface absorbs the heat because of a temperature differentialbetween the heat-absorbing surface and the surface of the heat sourcewith which it is in contact. Thus, heat from the heat source enters intothe accommodating cavity 35 via the heat absorbing surface 13. Becausethe first substrate 10 is made of a very dense and highly heatconductive material, conduction of heat into the accommodating cavity 35is very efficient. After the heat enters into the accommodating cavity35, the working fluid 40 in the capillary micro-structure layer 30 atthe bottom of the accommodating cavity 35 absorbs the heat and is thenvaporized to move to the top portion of the accommodating cavity 35.Then, the heat of the working fluid 40 is released in the top portion ofthe accommodating cavity 35 upon condensation where the heat is thenabsorbed by the second substrate 20 and subsequently dissipated to theoutside environment via the heat dissipating surface of the secondsubstrate 20. The efficiency of heat dissipating is also improvedthrough the highly heat conductive material of the second substrate 20.

As the heat is dissipated via the heat dissipating surface 23, theevaporated gas from the working fluid 40 is condensed into liquid.Because of gravity and the capillary force of the capillarymicro-structure layer 30, said liquid is pulled down to the bottom ofthe accommodating cavity 35 to be vaporized again, thus formingcirculation. The description above is the heat dissipating theory of theheat dissipating apparatus of the present invention, which has a highheat dissipating efficiency and complies with the heat dissipatingrequirements of electronic devices.

It should be apparent to those skilled in the art that the abovedescription is only illustrative of specific embodiments and examples ofthe invention. The invention should therefore cover variousmodifications and variations made to the herein-described structure andoperations of the invention, provided they fall within the scope of theinvention as defined in the following appended claims.

1. A heat dissipating apparatus having a micro-structure, comprising: a highly heat conductive member comprised of a highly heat conductive material, and having an accommodating cavity formed therein, wherein an inner wall of the accommodating cavity comprises a structured pattern, said highly heat conductive member further comprising a heat absorbing surface defined on an outer surface thereof, for being in contact with a heat source and absorbing heat generated by the heat source, and a heat dissipating surface defined on another outer surface thereof and opposite to the heat absorbing surface, for dissipating the heat to an outside environment; a micro-structure layer formed on the structured pattern, wherein the micro-structure layer is made of the highly heat conductive material; and a working fluid that fills the accommodating cavity, wherein at least a portion of the working fluid at a position close to the heat absorbing surface will absorb the heat from the heat absorbing surface causing the portion of the working fluid to vaporize, and wherein the vaporized working fluid coveys the absorbed heat to a position close to the heat dissipating surface, causing the absorbed heat to be released to the heat dissipating surface, thereby causing the vaporized working fluid to condense, with the condensed portion of the working fluid moving back to the position close to the heat absorbing surface due to gravity and capillary force.
 2. The heat dissipating apparatus as claimed in claim 1, wherein the highly heat conductive member is comprised of two high heat conductive substrates, each having the micro-structure layer formed thereon; further comprising a ring-shaped frame arranged between the two high heat conductive substrates for enlarging the accommodating cavity, and being disposed only at a periphery of the two high heat conductive substrates.
 3. The heat dissipating apparatus as claimed in claim 1, wherein the micro-structure layer is a capillary structure layer.
 4. The heat dissipating apparatus as claimed in claim 3, wherein the capillary structure layer is selected from the group consisting of a plurality of parallel grooves or a mesh structure.
 5. The heat dissipating apparatus as claimed in claim 1, wherein the highly heat conductive material is selected from the group consisting of copper, silver, and aluminum.
 6. The heat dissipating apparatus as claimed in claim 1, wherein the highly heat conductive member is one selected from the group consisting of a copper block, a silver block, and an aluminum block.
 7. The heat dissipating apparatus as claimed in claim 1, wherein the working fluid is one selected from the group consisting of liquid water, acetone, liquid nitrogen, and ethanol.
 8. The heat dissipating apparatus as claimed in claim 1, wherein the micro-structure layer covers an entire surface area defining the accommodating chamber.
 9. The heat dissipating apparatus as claimed in claim 1, wherein the highly heat conductive member is comprised of two high heat conductive substrates; further comprising a ring-shaped frame arranged between the two high heat conductive substrates for enlarging the accommodating cavity, and being disposed only at a periphery of the two high heat conductive substrates.
 10. The heat dissipating apparatus as claimed in claim 1, wherein the highly heat conductive member is comprised of two high heat conductive substrates each having the micro-structure layer formed thereon.
 11. A heat dissipating apparatus having a micro-structure, comprising: a highly heat conductive member comprised of a highly heat conductive material, and having an accommodating cavity formed therein, wherein an inner wall of the accommodating cavity comprises a structured pattern, said highly heat conductive member further comprising a heat absorbing surface defined on an outer surface thereof, for being in contact with a heat source and absorbing heat generated by the heat source, and a heat dissipating surface defined on another outer surface thereof and opposite to the heat absorbing surface, for dissipating the heat to an outside environment, the highly heat conductive member being comprised of two high heat conductive substrates; a ring-shaped frame arranged between the two high heat conductive substrates for enlarging the accommodating cavity; a micro-structure layer formed on the structured pattern, wherein the micro-structure layer is made of the highly heat conductive material, the micro-structure layer being a capillary structure layer selected from the group consisting of a plurality of parallel grooves or a mesh structure; and a working fluid that fills the accommodating cavity, the working fluid being selected from the group consisting of liquid water, acetone, liquid nitrogen, and ethanol, wherein at least a portion of the working fluid at a position close to the heat absorbing surface will absorb the heat from the heat absorbing surface causing the portion of the working fluid to vaporize, and wherein the vaporized working fluid coveys the absorbed heat to a position close to the heat dissipating surface, causing the absorbed heat to be released to the heat dissipating surface, thereby causing the vaporized working fluid to condense, with the condensed portion of the working fluid moving back to the position close to the heat absorbing surface due to gravity and capillary force.
 12. A heat dissipating apparatus having a micro-structure, comprising: a highly heat conductive member comprised of first and second high heat conductive substrates, each being formed from a highly heat conductive material, said first and second substrates each having an opening, and an inner surface in the opening with a plurality projections formed thereon, said first and second substrates being joined together so that the respective openings face each other and are in communication with each other, to form a completely enclosed accommodating cavity, the plurality of projections on the inner surface defining a structured pattern, said highly heat conductive member further comprising a heat absorbing surface defined on an outer surface thereof, for being in contact with a heat source and absorbing heat generated by the heat source, and a heat dissipating surface defined on another outer surface thereof and opposite to the heat absorbing surface, for dissipating the heat to an outside environment; a micro-structure layer formed on the entire inner surface of the first and second substrates, wherein the micro-structure layer is made of the highly heat conductive material; and a working fluid that fills the accommodating cavity, wherein at least a portion of the working fluid at a position close to the heat absorbing surface will absorb the heat from the heat absorbing surface causing the portion of the working fluid to vaporize, and wherein the vaporized working fluid coveys the absorbed heat to a position close to the heat dissipating surface, causing the absorbed heat to be released to the heat dissipating surface, thereby causing the vaporized working fluid to condense, with the condensed portion of the working fluid moving back to the position close to the heat absorbing surface due to gravity and capillary force. 